I doubt the term was intended deliberately as a racist term, even though it is. My GCSE Electronics teacher used the decidedly less racist "Richard of York gave battle vanely"; of course, it omits the first two and last two words, and vanely isn't an actual word (just changed from in vain to vanely because there's no indigo in component colour codes.) But it was good enough for me to remember the "main sequence" as it were. GCSE Electronics in this country is a good introduction to electronics and more teachers are sorely needed. Most schools don't do it. I was lucky to be near one that offered it.
I liked my electronics teacher (Mr. Goldthorpe); he had good electronics knowledge (good enough for GCSE), but the combination of actually building something real on a soldered prototype board, and testing and debugging it was fantastic experience, and he taught me a lot. I got an A. Not A*, probably because I didn't focus enough on my documentation.
A-Level electronics is a joke - everything on prototype board, for example. Nothing soldered. In the induction in my first week in Uni, only a couple of kids had ever soldered in their life, and because they did, their project boards worked (proper PCBs.) I had a fantastic teacher - Dr. Rutherford - but the syllabus really let him down. We don't discuss bipolar transistors any more for example, because apparently they aren't used enough in digital circuits (and about half the course is on digital circuits.)
The teacher should have been disciplined, and told not to say it again, especially not around students. I think firing is too harsh.